In order to obtain a product having a satisfactory quality in the processing of web materials, e.g. in connection with printing, a high accuracy is required as regards an accurate positioning, when the web material is fed into processing machines. When it is the matter of printing, the processing machines can be printing machines.
When the material is fed between rolls, it generally is pretensioned and stretched, which results in a varying length in connection with variations in e.g. web tension and coefficient of elasticity. The elongation of the web material varies with web width, web thickness, moisture, material quality etc. A high product quality requires knowledge of the elongation of the web material in various processing phases and particularly in critical processing phases.
An example of this is the printing on a running paper web, and it is important that the print on forms obtains a predetermined length after the printing. This is particularly important in connection with the preparation of multi-sheet sets, which comprise a plurality of assembled forms, designed e.g. for the simultaneous typing of invoices, shipping notes, order confirmations, etc. Also, in case these multi-sheet sets of assembled forms shall be printed in a remaliner-fed printer, the hole punching for the remaliner-feeding must have an accurate distance between the holes in accordance with the length of the forms. It is difficult to keep the correct length on printed web materials and this is often evident in multi-sheet sets of assembled forms, designed for remaliner-feeding. In these sets some sheets are often stretched and some are wavy, since they are "extended" (in comparison with the rest of the sheets). The sets of assembled forms in this way become unneccesarily thick with air inclusions around the wavy sheets.